1. Fields of the Invention
The present invention relates to a method of manufacturing a phosphor, especially to a method of manufacturing an oxynitride phosphor.
2. Descriptions of Related Art
In developed countries worldwide, white-light LED (light emitting diode)-based lighting will gradually replace conventional light sources due to energy savings, carbon reduction, and environment protection. The advantages of LED include compact size, low power consumption, long life time, low heat emission, and short reaction time. LED is easy to install in equipment, of low heat radiation, and used for high frequency operation and over 100 thousand hours. It uses only one-eighths or one-tenths power in comparison with conventional light bulbs and a half power compared with fluorescent lights. LED overcomes a plurality of shortcomings of incandescent bulbs. Thus the white-light LED is a new light source for illumination and displays of the 21st century. It is called green light source due to its features of energy saving and environment protection.
Refer to U.S. Pat. No. 5,998,925 applied by Japanese Nichia Corporation filed in 1996, a light emitting diode (LED) employs a gallium nitride compound semiconductor element emitting blue light and a garnet phosphor activated with cerium in combination. The phosphor is preferably yttrium-aluminum-garnet fluorescent material (YAG phosphor) activated with cerium (YAG:Ce). With this configuration, the LED can emit white light by blending blue light emitted by the light emitting components and yellow light emitted by the phosphor excited by the blue light. The nitride phosphors available now have better thermal resistance and water resistance yet the cost is high. As to oxide phosphors, the cost is low but it has poor thermal stability and poor water resistance. Thus oxynitride phosphors have received considerable attention compared to the existing nitride and oxide phosphors. There is no nitride with extreme air-sensitivity used in a precursor for synthesis of the oxynitride phosphors. Using a part of oxides reduces the synthesis temperature. Moreover, the oxynitride phosphors have good stability similar to that of the nitrides. The oxynitride phosphors have advantages of both oxides and nitrides. Thus a plurality of oxynitride phosphors including β-SiAlON, MSi2O2N2 (M=Ca, Sr, Ba), etc. has been provided in recent years.
In 2009, Mitsubishi Chemical Corporation has also applied for the patent with Pub. No. WO/2009/017206, App. No. PCT/JP2008/063802 filed on Jul. 31, 2008 and the title is “PHOSPHOR AND METHOD FOR PRODUCING THE SAME, CRYSTALLINE SILICON NITRIDE AND METHOD FOR PRODUCING THE SAME, PHOSPHOR-CONTAINING COMPOSITION, LIGHT-EMITTING DEVICE USING THE PHOSPHOR, IMAGE DISPLAY DEVICE, AND ILLUMINATING DEVICE”. The sample revealed in this patent is synthesized under normal pressure and a pure product is obtained by using pre-treated silicon nitride (Si3N4) precursor.